Start by preheating your oven to 350°F (175°C) for efficient baking.

Prepare your 6-inch cake pan by spraying with non-stick cooking spray and lining the bottom with a parchment paper circle for easy release.

Cream the butter and sugar in a medium bowl using an electric mixer until light and fluffy, about 1-2 minutes.

Blend in the egg and vanilla extract until the mixture is smooth and well-combined.

In a separate bowl, whisk together the flour, salt, and baking soda. Gradually mix half of the dry ingredients into the batter, followed by half of the milk and vinegar. Repeat with the remaining halves until just combined.

Transfer the batter into the prepared pan, smoothing the top, and bake for 37 minutes or until a cake tester comes out clean.

Allow the cake to cool in the pan on a wire rack before removing it and peeling off the parchment paper.

For the buttercream, whip the butter until fluffy, then gradually add powdered sugar, vanilla, and heavy cream until you achieve a smooth, spreadable consistency.

Frost the cake with a generous layer of buttercream, applying a crumb coat first if the cake was previously frozen.

Fill a piping bag fitted with a 1M tip with the remaining buttercream and pipe roses around the edge of the cake, starting from the center and spiraling outwards.